Hodgdon 777 is not a black powder duplicate. That is, unlike Pyrodex, you should not use it volume-for-volume against black powder.
While 40 grs. of FFFG black powder can safely be used in the Remington .44, under a ball, the same volume of Hodgdon 777 would generate pressures higher than desired or safe.
Hodgdon advises to reduce all loads 15 percent, when using 777.
I first tried 777 in my Uberti-made Remington 1858 Army a few years back. It's powerful stuff.
Hodgdon 777 should not be used in any brass-framed cap and ball revolver. Brass-framed guns lack the strength to withstand the higher pressures.
Used with manufacturer recommendations, in a steel-framed cap and ball sixgun, Hodgdon 777 is perfectly safe. I use it on occasion and it's good stuff. I haven't found it as accurate at real black powder, but then I've never found any powder as accurate as black, especially in FFFG grade.